1. Field of the Invention
The present invention relates to microscope apparatuses, and more particularly, to a microscope apparatus using a phase-modulating spatial light modulator.
2. Description of the Related Art
In the field of biological microscopy, there is known a fluorescence observation method which discovers biological functions by using fluorescence imaging and sampling operation with light stimulation (such as photoactivation, photoconversion, cell function control and activation) in combination. In the fluorescence observation method, two-photon excitation with use of a laser beam is also often used because the two-photon excitation enables observation of the deep regions of a biological organism and is also less destructive to the biological organism.
With the above-mentioned fluorescence observation method, microscopes are required to have a function to change the pattern (shape, size, the number of spots, etc.) of light irradiating a sample and the irradiation position thereof arbitrary at high speed depending on the sample and its application. This function can be implemented by using a phase-modulating spatial light modulator (hereinafter referred to as SLM) placed at a position optically conjugate with a pupil position of an objective lens (hereinafter referred to as a pupil conjugate position). The apparatuses relating to such technologies are disclosed, for example, in Japanese Patent Laid-Open No. 2006-72280 and U.S. Pat. No. 7,733,564.
According to the optical apparatus including a phase-modulating SLM placed at the pupil conjugate position of the objective lens, the phase-modulating SLM modulates the phase of a laser beam at the pupil conjugate position to control the wave front, which makes it possible to form an arbitrary light pattern on a sample plane via the objective lens that functions as a Fourier transform lens. It also becomes possible to adjust the irradiation position in an optical axis direction of the objective lens and to perform aberration correction of the objective lens.
In the fluorescence observation method, laser beams of various wavelengths are used as excitation light depending on fluorescent materials. With the laser beam from a light source, a beam divergence (spread angle) and a beam waist position are changed depending on an emitted wavelength and individual difference of the laser beam source. The change in divergence and beam waist position, which influences a beam diameter and a degree of convergence of the laser beam at the pupil position of the objective lens, produces various undesirable consequences such as loss in the amount of light due to the beam diameter being excessively large with respect to the pupil diameter, deterioration in resolution due to the beam diameter being excessively small, and change in irradiation position due to variations in the degree of convergence of the laser beam.
Moreover in the fluorescence observation method, while various objective lenses are used depending on observation objects and other factors, they each have different aberration characteristics and pupil diameter. The difference in aberration characteristics and pupil diameter of the objective lens produces various undesirable consequences such as deterioration in focusing performance due to insufficient aberration correction, loss in the amount of light due to the beam diameter being excessively large with respect to the pupil diameter, and deterioration in resolution due to the beam diameter being excessively small.
Thus, in the microscope apparatuses for use in the fluorescence observation method, due consideration needs to be given to the characteristics of the objective lens and the laser beam source to be used (or the wavelength thereof), so that desired performance can be achieved.